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          <h1 class="post-title" itemprop="name headline">论pyqt 编码的蹊跷——QTextStream、QString、string、unicode相关</h1>
        

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        <p><strong>环境：</strong>Pyqt4.8 32位，python2.7.3 32位<br>你是不是每次看到什么字符编码、文件编码和字符串类型，都会有些懵逼呢？反正我有点，以前情况不复杂，这次遇到个坑，特此记录下。</p>
<h4 id="背景："><a href="#背景：" class="headerlink" title="背景："></a>背景：</h4><p>从<strong>qrc</strong>文件中读取某文本文件，然后解析成json，并显示在Qt控件上。该文件以<strong>utf-8</strong>编码，并保存有<strong>中文</strong>，对，就是这个中文的引出的话题,不是中文也就不复杂了……  </p>
<h4 id="分析："><a href="#分析：" class="headerlink" title="分析："></a>分析：</h4><pre><code>1. 从rcc编译的qrc文件中读取文件，也就意味着无法使用python的标准代码：
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">with</span> open(file_path) <span class="keyword">as</span> f:</span><br><span class="line">	content = json.load(f)</span><br><span class="line">	<span class="keyword">print</span> content</span><br></pre></td></tr></table></figure>

别无选择，只能使用QFile。
2. 说到QFile，自然要用到QTextStream了。
3. 再使用python unicode()函数将str对象解码。
4. 最后使用json库loads()方法，解析成json对象。
基本代码是这样的：  
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">read_file</span><span class="params">(path)</span>:</span></span><br><span class="line">	<span class="keyword">try</span>:</span><br><span class="line">		f = QtCore.QFile(path)</span><br><span class="line">		<span class="keyword">if</span> <span class="keyword">not</span> f.open(QtCore.QFile.ReadOnly | QtCore.QFile.Text):</span><br><span class="line">			<span class="keyword">return</span> <span class="string">""</span></span><br><span class="line">		ts = QtCore.QTextStream(f)</span><br><span class="line">		tsData = ts.readAll()</span><br><span class="line">		content = unicode(tsData, <span class="string">"utf-8"</span>, <span class="string">"ignore"</span>)</span><br><span class="line">		<span class="keyword">return</span> json.loads(content)</span><br><span class="line">	<span class="keyword">except</span>:</span><br><span class="line">		<span class="keyword">import</span> traceback</span><br><span class="line">		traceback.print_exc()</span><br><span class="line">	<span class="keyword">finally</span>:</span><br><span class="line">		f.close()</span><br></pre></td></tr></table></figure>

最后发现报错了……
ValueError: Invalid control character at: line 14 column
5. 尝试将tsData先转换为utf-8编码，结果还是报错……
还尝试着直接使用str()等等方法，包括网上的一些技巧，比如：json.loads(content, strict=False)，都失败了……</code></pre><h4 id="解决及总结："><a href="#解决及总结：" class="headerlink" title="解决及总结："></a>解决及总结：</h4><pre><code>1. QTextStream在读取文本文件时，会默认使用Local的字符编码，如果不指定编码，会使后续的处理寸步难行……
后续有个官方链接说明了
For Python v2 the following conversions are done by default.
If Qt expects a char *, signed char * or an unsigned char * (or a const version) then PyQt4 will accept a unicode or QString that contains only ASCII characters, a str, a QByteArray, or a Python object that implements the buffer protocol.
If Qt expects a char, signed char or an unsigned char (or a const version) then PyQt4 will accept the same types as for char *, signed char * and unsigned char * and also require that a single character is provided.
If Qt expects a QString then PyQt4 will accept a unicode, a str that contains only ASCII characters, a QChar or a QByteArray.
If Qt expects a QByteArray then PyQt4 will accept a unicode that contains only Latin-1 characters, or a str
2. Unicode()在不指定encoding参数的情况下，有两种操作。如果字符串是str对象，则会调用str()，也就是使用python默认的ascci编码来解码。如果已经是Unicode对象则不会任何附加操作。
If no optional parameters are given, unicode() will mimic the behaviour of str() except that it returns Unicode strings instead of 8-bit strings. More precisely, if object is a Unicode string or subclass it will return that Unicode string without any additional decoding applied.
所以在这里，我们需要指定utf-8的编码格式，才能转化为unicode对象。
最后代码如下：
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@contextmanager</span></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">read_file</span><span class="params">(path)</span>:</span></span><br><span class="line">	<span class="keyword">try</span>:</span><br><span class="line">		f = QtCore.QFile(path)</span><br><span class="line">		<span class="keyword">if</span> f.open(QtCore.QFile.ReadOnly | QtCore.QFile.Text):</span><br><span class="line">			ts = QtCore.QTextStream(f)</span><br><span class="line">			ts.setCodec(<span class="string">"utf-8"</span>)</span><br><span class="line">			tsData = ts.readAll()</span><br><span class="line">			content = unicode(tsData.toUtf8(), <span class="string">"utf-8"</span>, <span class="string">"ignore"</span>)</span><br><span class="line">			<span class="keyword">yield</span> json.loads(content)</span><br><span class="line">		<span class="keyword">else</span>:</span><br><span class="line">			<span class="keyword">yield</span> <span class="string">""</span></span><br><span class="line">	<span class="keyword">except</span>:</span><br><span class="line">		<span class="keyword">import</span> traceback</span><br><span class="line">		traceback.print_exc()</span><br><span class="line">		<span class="keyword">yield</span> <span class="string">""</span></span><br><span class="line">	<span class="keyword">finally</span>:</span><br><span class="line">		f.close()</span><br></pre></td></tr></table></figure></code></pre><p>有个需要注意的地方，如果要gui控件能正常显示中文，<code>content = unicode(tsData.toUtf8(), &quot;utf-8&quot;, &quot;ignore&quot;)</code>中的<strong>toUtf8()</strong>是必不可少，不然会显示为乱码。 </p>
<h4 id="总结："><a href="#总结：" class="headerlink" title="总结："></a>总结：</h4><p>一句话总结：<strong>区分什么是编码，什么是对象，Unicode是中转对象，str-&gt;unicode是解码，unicode-&gt;str是编码。</strong><br>不知在谁的blog上看到的了，很形象，很深刻……谢谢这样仁兄！</p>
<hr>
<p>相关链接：<br><a href="http://pyqt.sourceforge.net/Docs/PyQt4/gotchas.html" target="_blank" rel="noopener">PyQt 4.12 Reference Guide</a></p>

      
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